A conventional window blind device includes a headrail, a bottomrail, a window shade, and a sprig motor. The spring motor includes a frame and a plurality of wheel gears. The wheel gears are rotatably mounted in the frame, and are coupled to the bottomrail so as to permit the bottomrail to be displaced between uppermost and lowermost positions.
U.S. Pat. No. 6,761,203 B1 discloses a window blind, in which a frame includes a casing part and a cover part. To produce the casing part and the cover part, it is necessary to prepare two different forming molds. In addition, screws are needed for securing the cover part to the casing part.